1. Technical Field
The present invention relates to an optical device and an image display apparatus.
2. Related Art
Projectors and head-mounted displays are known as projection type image display apparatuses in which images are generated by controlling the wavelength or intensity of light for each pixel in image forming elements including two-dimensionally arrayed pixels and the images are expanded and displayed by optical systems such as lenses. Liquid crystal elements or organic EL elements are used as the image forming elements and the resolutions of these elements are designed to be improved every year.
At present, in markets of image display apparatuses, products with resolutions called full high-visions have been spread. In future, these products are expected to migrate to, for example, products with high resolutions called 4K or 8K (super high-visions).
As one of the methods of realizing such high-resolution display, there is a method of using a pixel shift device (pixel shifter) shifting a projection position of an image generated by an image forming element. As the pixel shift device, a device shifting an optical path using refraction (optical modulation) in an optical element is known.
For example, JP-A-2009-171784 discloses an oscillation driving device that includes a flap in which a glass transmitting projection light of an image forming apparatus, a coil, and a belt-like plate spring bent by a propulsion force generated in the coil and generating a reactive force are fitted. The belt-like plate spring includes a twisting beam portion and supports the flap so that the flap can be oscillated. The twisting beam portion is connected to a bending beam portion formed to be vertical to an oscillation axis center. In the oscillation driving device, when a current flows in the coil, a propulsion force is generated and the flap in which the glass is fitted is oscillated against a spring reactive force of the belt-like plate spring. By oscillating the glass in this way, it is possible to shift a projection position of the light transmitted through the glass.
However, in such an oscillation driving device, the belt-like plate spring which is spread in a planar shape and for which a given area is necessary is used to oscillate the flap. Therefore, there is a problem that it is difficult to decrease an occupation area of the device.
On the other hand, in order to decrease the occupation area, a bending beam portion formed to be vertical to the oscillation axis center can be considered to be omitted in the oscillation driving device disclosed in JP-A-2009-171784. In this case, however, since it is necessary to oscillate the twisting beam portion, it is necessary to lengthen the length of the twisting beam portion sufficiently in order to obtain a predetermined oscillation frequency while sufficiently decreasing generated stress. Consequently, the twisting beam portion may be lengthened.